Contributions to a theory of reinforcement in human behavior are sought at two levels: (1) A general theory interpreting reinforcement in terms of stimulus amplifiers, feedback processes, and a hierarchical association model for memory factors in conditioning; (2) extension of the theory to human behavior by relating basic mechanisms to information processing concepts. Experimental researches are aimed at working out in detail the way in which verbal and memory capacities of normal human beings modify motivational and reinforcement mechanisms. Principal lines of research include: (1) Clarifying the way in which information concerning event probabilities is stored in memory and how this information serves as the basis for choice; (2) generalizing the classical multiple-choice situation to include the process of recall of choice alternatives and relating probability learning to current work on memory for frequency; (3) continuing current efforts to separate stimulus and response selection experimentally, with particular attention to the role of reinforcement in modifying stimulus salience or attention value as distinguished from its role in the acquisition of information concerning choice-outcome relationships; (4) complementing current work on hypothesis selection by studies of the way in which hypotheses and rules gain and maintain control of behavior and by relating the availability and retrievability of rules to stimulus and temporal variables; (5) conducting some experiments in parallel on human subjects and subhuman primates in order to facilitate the task of relating concepts of reinforcement in human behavior to basic learning processes.